I spend a lot of time in Greece, a few weeks every year for the last 12 years.
Favourite island is Alonissos, one of the Sporades along with Skiathos & Skopelos, all joined up by ferries. Love them all.
Thassos is also very good, that was a new one last year. I drove to the summit of the island in a manky jeep, it was highly risky, edging around boulders on single track mountain roads.
The Mani on the mainland is great, very spaghetti western. Banditry, tower houses, goats and eagles. Patrick Leigh Fermor spent his later days there, in Kardamyli.
I used to have a low opinion of Greek food but its simplicity really grows on you. Same with the wine.